[The variability of the QRS loop in the orthogonal lead system of frank and schmitt (SVEC III) (author's transl)].

A method has been previously described, to test the accuracy of lead fields. This method is used here to compare in 7 persons the relative validity of the two orthogonal lead systems of Frank and Schmitt (SVECC III). The variables the variation of which characterizes the validity of the systems, are the spatial position (represented by the spatial angles of the normal of the broadside view) and the variations in shape of the vector loops. The latter are measured by a comparison of the length of vectors in a distance of 5 degrees, starting with the maximal vector and proceeding from here to both sides. The vectors of loops in two different heart positions are compared by means of their correlation coefficients, and one of the loops is rotated in space as long as this correlation coefficient reaches a maximum. The data are handled by a computer. The optimal correlation coefficients, the regression coefficients and the differences in the spatial angles of the planes, in which the loops show their broadside view, are compared. The Frank system has a significantly lower variability of these values, by extreme dislocations of the heart, either by respiratory or by positional dislocations.